Question

An AP has 10 terms. If its first and last terms are 5 and 50 respectively, then its sum is

• A. 275
• B. 325
• C. 425

Answer 1

The correct option is A 275

We know that sum to n terms of an AP is $\frac{n}{2}(a+l)$, where a and l are the first and last terms respectively, and n is the number of terms.

Given that an AP has four terms, first and last terms are 5 and 50 respectively.
$n=10,a=5,l=50$
$S_n=\frac{n(a+l)}{2}$
$S_n=\frac{10(5+50)}{2}$
$S_n=275$